In refrigeration systems, a refrigerant gas is compressed in a compressor unit. Heat generated by the compression is then removed generally by passing the compressed gas through a water or air cooled condenser coil. The cooled, condensed gas is then allowed to rapidly expand into an evaporator coil where the gas becomes much colder, thus cooling the coil and the inside of the refrigeration system box around which the coil is placed.
Life Science researchers have a need for ultra low temperature (“ULT”) storage chambers to store products such as living organisms, biologically active reagents, and the like. As these products may die or become biologically inactive when improperly warmed, these researchers also need to minimize any product warm-up. In this regard, generally, sensors are utilized to determine whether the inside of the refrigeration system box or cabinet is within a predetermined temperature range. In response to sensed temperatures being outside this predetermined temperature range, a controller typically modulates the compressor to effect an appropriate temperature change. For example, if the temperature rises above the predetermined temperature range, the controller may modulate the compressor to turn on or increase speed.
A problem, which has arisen with such ULT freezers, is that when the sensor fails, the controller may improperly modulate the compressor and the temperature may deviate outside the predetermined temperature range. Known ULT freezers typically include an alert system designed to notify a user of potential problems. Often, these freezers also include a default operation. This default operation is generally only appropriate for a relatively narrow range of operating conditions. As these ULT freezers are commonly located in remote areas, the alert system may go un-noticed for an extended period of time. Thus, if the operational conditions are outside the relatively narrow range for which the default operation is optimized, the temperature may deviate outside the predetermined temperature range and the contents of the ULT freezer may be destroyed.
In addition, temperature deviations outside the predetermined temperature range are not only undesirable for the contents, but lowering the temperature below the predetermined temperature range places increased loads on the refrigeration unit as it must operate on a more continuous basis than it was designed. This increased load may decrease compressor life or cause compressor failure.
The present invention overcomes the above mentioned disadvantages to a great extent, and provides many additional advantages which shall become apparent as described below.